Frankfurt

Frankfurt needs a full day: the Römer (medieval city hall) and the rebuilt old town on one, the Alte Oper next to the skyscraper financial district -nicknamed «Mainhattan»- on the other end. April-September has the best weather. It's expensive, with high hotel prices reflecting its weight as a business and international trade fair hub. It's home to the European Central Bank and Germany's only skyscraper skyline, an unusual contrast to the country's other historic cities that makes it the most «American»-looking German city at first glance.